1. Field of the Invention
The present invention relates to a method for providing hearing assistance to a user; it also relates to a corresponding system. In particular, the invention relates to a system comprising a transmission unit comprising a microphone arrangement for capturing audio signals, a receiver unit, and means for stimulating the hearing of the user wearing the receiver unit, with the audio signals being transmitted via a wireless audio link from the transmission unit to the receiver unit.
2. Description of Related Art
Usually in such systems the wireless audio link is an FM radio link. The benefit of such systems is that sound captured by a remote microphone at the transmission unit can be presented at a high sound pressure level to the hearing of the user wearing the receiver unit at his ear(s).
According to one typical application of such wireless audio systems, the stimulating means is a loudspeaker which is part of the receiver unit or is connected thereto. Such systems are particularly helpful for being used in teaching normal-hearing children suffering from auditory processing disorders (APD), wherein the teacher's voice is captured by the microphone of the transmission unit, and the corresponding audio signals are transmitted to and are reproduced by the receiver unit worn by the child, so that the teacher's voice can be heard by the child at an enhanced level, in particular with respect to the background noise level prevailing in the classroom. It is well known that presentation of the teacher's voice at such enhanced level supports the child in listening to the teacher.
Usually in such systems the audio signals received by the receiver are amplified at a given constant gain for being reproduced by the output transducer. FIG. 5 shows an example of a block diagram of such a conventional receiver unit 103 comprising an antenna 123, an FM radio receiver 124, an amplifier 138 operating at constant gain, a power audio amplifier 137 for a loudspeaker 136, and a manual volume control 135 acting on the power amplifier 137. Such receiver unit has as a drawback that due to the constant gain the audio signals received from the remote microphone are amplified irrespective of whether they are desired by the user (e.g. if the teacher is silent there is no benefit to the user by receiving audio signals from the remote microphone, which then may consist primarily of noise).
According to another typical application of wireless audio systems the receiver unit is connected to or integrated into a hearing instrument, such as a hearing aid. The benefit of such systems is that the microphone of the hearing instrument can be supplemented or replaced by the remote microphone which produces audio signals which are transmitted wirelessly to the FM receiver and thus to the hearing instrument. In particular, FM systems have been standard equipment for children with hearing loss in educational settings for many years. Their merit lies in the fact that a microphone placed a few inches from the mouth of a person speaking receives speech at a much higher level than one placed several feet away. This increase in speech level corresponds to an increase in signal-to-noise ratio (SNR) due to the direct wireless connection to the listener's amplification system. The resulting improvements of signal level and SNR in the listener's ear are recognized as the primary benefits of FM radio systems, as hearing-impaired individuals are at a significant disadvantage when processing signals with a poor acoustical SNR.
Most FM systems in use today provide two or three different operating modes. The choices are to get the sound from: (1) the hearing instrument microphone alone, (2) the FM microphone alone, or (3) a combination of FM and hearing instrument microphones together.
Usually, most of the time the FM system is used in mode (3), i.e. the FM plus hearing instrument combination (often labeled “FM+M” or “FM+ENV” mode). This operating mode allows the listener to perceive the speaker's voice from the remote microphone with a good SNR while the integrated hearing instrument microphone allows to listener to also hear environmental sounds. This allows the user/listener to hear and monitor his own voice, as well as voices of other people or environmental noise, as long as the loudness balance between the FM signal and the signal coining from the hearing instrument microphone is properly adjusted. The so-called “FM advantage” measures the relative loudness of signals when both the FM signal and the hearing instrument microphone are active at the same time. As defined by the ASHA (American Speech-Language-Hearing Association 2002), FM advantage compares the levels of the FM signal and the local microphone signal when the speaker and the user of an FM system are spaced by a distance of two meters. In this example, the voice of the speaker will travel 30 cm to the input of the FM microphone at a level of approximately 80 dB-SPL, whereas only about 65 dB-SPL will remain of this original signal after traveling the 2 m distance to the microphone in the hearing instrument. The ASHA guidelines recommend that the FM signal should have a level 10 dB higher than the level of the hearing instrument's microphone signal at the output of the user's hearing instrument.
When following the ASHA guidelines (or any similar recommendation), the relative gain, i.e. the ratio of the gain applied to the audio signals produced by the FM microphone and the gain applied to the audio signals produced by the hearing instrument microphone, has to be set to a fixed value in order to achieve e.g. the recommended FM advantage of 10 dB under the above-mentioned specific conditions. Accordingly, heretofore—depending on the type of hearing instrument used—the audio output of the FM receiver has been adjusted in such a way that the desired FM advantage is either fixed or programmable by a professional, so that during use of the system the FM advantage—and hence the gain ratio—is constant in the FM+M mode of the FM receiver.
EP 0 563 194 B1 relates to a hearing system comprising a remote microphone/transmitter unit, a receiver unit worn at the user's body and a hearing aid. There is radio link between the remote unit and the receiver unit, and there is an inductive link between the receiver unit and the hearing aid. The remote unit and the receiver unit each comprise a microphone, with the audio signals of theses two microphones being mixed in a mixer. A variable threshold noise-gate or voice-operated circuit may be interposed between the microphone of the receiver unit and the mixer, which circuit is primarily to be used if the remote unit is in a line-input mode, i.e. the microphone of the receiver then is not used.
WO 97/21325 A1 relates to a hearing system comprising a remote unit with a microphone and an FM transmitter and an FM receiver connected to a hearing aid equipped with a microphone. The hearing aid can be operated in three modes, i.e. “hearing aid only”, “FM only” or “FM+M”. In the FM+M mode the maximum loudness of the hearing aid microphone audio signal is reduced by a fixed value between 1 and 10 dB below the maximum loudness of the FM microphone audio signal, for example by 4 dB. Both the FM microphone and the hearing aid microphone may be provided with an automatic gain control (AGC) unit.
WO 2004/100607 A1 relates to a hearing system comprising a remote microphone, an FM transmitter and left-and right-ear hearing aids, each connected with an FM receiver. Each hearing aid is equipped with a microphone, with the audio signals from remote microphone and the respective hearing aid microphone being mixed in the hearing aid. One of the hearing aids may be provided with a digital signal processor which is capable of analyzing and detecting the presence of speech and noise in the input audio signal from the FM receiver and which activates a controlled inverter if the detected noise level exceeds a predetermined limit when compared to the detected level, so that in one of the two hearing aids the audio signal from the remote microphone is phase-inverted in order to improve the SNR.
WO 02/30153 A1 relates to a hearing system comprising an FM receiver connected to a digital hearing aid, with the FM receiver comprising a digital output interface in order to increase the flexibility in signal treatment compared to the usual audio input parallel to the hearing aid microphone, whereby the signal level can easily be individually adjusted to fit the microphone input and, if needed, different frequency characteristics can be applied. However, is not mentioned how such input adjustment can be done.
Contemporary digital hearing aids are capable of permanently performing a classification of the present auditory scene captured by the hearing aid microphones in order to select the hearing aid operation mode which is most appropriate for the determined present auditory scene. Examples for such hearing aids with auditory scene analyses can be found in US2002/0037087, US2002/0090098, CA 2 439 427 A1 and US2002/0150264.
Usually FM or inductive receivers are equipped with a squelch function by which the audio signal in the receiver is muted if the level of the demodulated audio signal is too low in order to avoid user's perception of excessive noise due a too low sound pressure level at the remote microphone or due to a large distance between the transmission unit and the receiver unit exceeding the reach of the FM link, see for example U.S. Pat. No. 5,734,976 and EP 1 619 926 A1
It is an object of the invention to provide for a method and a system for providing hearing assistance to a user, wherein a remote microphone arrangement coupled by a wireless audio link to a receiver unit which provides the audio signals to means for stimulating the hearing of the user wearing the receiver unit is used and wherein the listening comfort, and in particular the signal-to-noise-ratio (SNR), of the audio signals from the microphone arrangement should be optimized at any time.
It is a further object of the invention to provide for a method and a system for providing hearing assistance to a user, wherein a remote first microphone arrangement coupled by a wireless audio link to a hearing instrument and a second microphone arrangement connected to or integrated into the hearing instrument are used and wherein the SNR of the audio signals from at least one of the first and second microphone arrangement should be optimized at any time.
According to the invention, these objects achieved by a method as defined in claim 1 and a system as defined in claim 55, and by a method as defined in claim 33 and a system as defined in claim 57, respectively.